17692203bc
Update links for the HA Guide conversion to RST. Change-Id: I9ac73929178a68d20a857c4223efdcdcc889528e
721 lines
32 KiB
XML
721 lines
32 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE section [
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<!ENTITY % openstack SYSTEM "../../common/entities/openstack.ent">
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%openstack;
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]>
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<section xmlns="http://docbook.org/ns/docbook"
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xmlns:xi="http://www.w3.org/2001/XInclude"
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xmlns:xlink="http://www.w3.org/1999/xlink"
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version="5.0"
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xml:id="arch-guide-architecture-overview">
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<?dbhtml stop-chunking?>
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<title>Architecture</title>
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<para>Hardware selection involves three key areas:</para>
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<itemizedlist>
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<listitem>
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<para>Compute</para>
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</listitem>
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<listitem>
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<para>Network</para>
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</listitem>
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<listitem>
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<para>Storage</para>
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</listitem>
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</itemizedlist>
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<para>Hardware for a general purpose OpenStack cloud
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should reflect a cloud with no pre-defined usage model,
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designed to run a wide variety of applications with
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varying resource usage requirements.
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These applications include any of the following:</para>
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<itemizedlist>
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<listitem>
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<para>
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RAM-intensive
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</para>
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</listitem>
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<listitem>
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<para>
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CPU-intensive
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</para>
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</listitem>
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<listitem>
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<para>
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Storage-intensive
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</para>
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</listitem>
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</itemizedlist>
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<para>Certain hardware form factors may better suit a general
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purpose OpenStack cloud due to the requirement for equal (or
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nearly equal) balance of resources. Server hardware must provide
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the following:</para>
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<itemizedlist>
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<listitem>
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<para>
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Equal (or nearly equal) balance of compute capacity (RAM and CPU)
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</para>
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</listitem>
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<listitem>
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<para>
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Network capacity (number and speed of links)
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</para>
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</listitem>
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<listitem>
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<para>
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Storage capacity (gigabytes or terabytes as well as Input/Output
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Operations Per Second (<glossterm>IOPS</glossterm>)
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</para>
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</listitem>
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</itemizedlist>
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<para>Evaluate server hardware around four conflicting
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dimensions:</para>
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<variablelist>
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<varlistentry>
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<term>Server density</term>
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<listitem>
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<para>A measure of how many servers can
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fit into a given measure of physical space, such as a
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rack unit [U].</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>Resource capacity</term>
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<listitem>
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<para>The number of CPU cores, amount of RAM,
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or amount of deliverable storage.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>Expandability</term>
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<listitem>
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<para>Limit of additional resources you can add to
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a server.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>Cost</term>
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<listitem>
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<para>The relative purchase price of the hardware
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weighted against the level of design effort needed to
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build the system.</para>
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</listitem>
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</varlistentry>
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</variablelist>
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<para>Increasing server density means sacrificing resource
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capacity or expandability, however, increasing resource
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capacity and expandability increases cost and decreases server
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density. As a result, determining the best server hardware for
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a general purpose OpenStack architecture means understanding
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how choice of form factor will impact the rest of the
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design. The following list outlines the form factors to
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choose from:</para>
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<itemizedlist>
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<listitem>
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<para>Blade servers typically support dual-socket
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multi-core CPUs. Blades also offer
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outstanding density.</para>
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</listitem>
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<listitem>
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<para>1U rack-mounted servers occupy only a single rack
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unit. Their benefits include high density, support for
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dual-socket multi-core CPUs, and support for
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reasonable RAM amounts. This form factor offers
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limited storage capacity, limited network capacity,
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and limited expandability.</para>
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</listitem>
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<listitem>
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<para>2U rack-mounted servers offer the expanded storage
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and networking capacity that 1U servers tend to lack,
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but with a corresponding decrease in server density
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(half the density offered by 1U rack-mounted
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servers).</para>
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</listitem>
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<listitem>
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<para>Larger rack-mounted servers, such as 4U servers,
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will tend to offer even greater CPU capacity, often
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supporting four or even eight CPU sockets. These
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servers often have much greater expandability so will
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provide the best option for upgradability. This means,
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however, that the servers have a much lower server
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density and a much greater hardware cost.</para>
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</listitem>
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<listitem>
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<para><emphasis>Sled servers</emphasis> are rack-mounted servers that support
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multiple independent servers in a single 2U or 3U
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enclosure. This form factor offers increased density
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over typical 1U-2U rack-mounted servers but tends to
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suffer from limitations in the amount of storage or
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network capacity each individual server
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supports.</para>
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</listitem>
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</itemizedlist>
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<para>The best form factor for server hardware
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supporting a general purpose OpenStack cloud is driven by
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outside business and cost factors. No single reference
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architecture applies to all implementations; the decision
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must flow from user requirements, technical
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considerations, and operational considerations. Here are some
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of the key factors that influence the selection of server
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hardware:</para>
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<variablelist>
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<varlistentry>
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<term>Instance density</term>
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<listitem>
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<para>Sizing is an important
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consideration for a general purpose OpenStack cloud.
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The expected or anticipated number of instances that
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each hypervisor can host is a common meter used in
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sizing the deployment. The selected server hardware
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needs to support the expected or anticipated instance
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density.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>Host density</term>
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<listitem>
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<para>Physical data centers have limited
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physical space, power, and cooling. The number of
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hosts (or hypervisors) that can be fitted into a given
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metric (rack, rack unit, or floor tile) is another
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important method of sizing. Floor weight is an often
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overlooked consideration. The data center floor must
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be able to support the weight of the proposed number
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of hosts within a rack or set of racks. These factors
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need to be applied as part of the host density
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calculation and server hardware selection.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>Power density</term>
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<listitem>
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<para>Data centers have a specified amount
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of power fed to a given rack or set of racks. Older
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data centers may have a power density as power as low
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as 20 AMPs per rack, while more recent data centers
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can be architected to support power densities as high
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as 120 AMP per rack. The selected server hardware must
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take power density into account.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>Network connectivity</term>
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<listitem>
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<para>The selected server hardware
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must have the appropriate number of network
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connections, as well as the right type of network
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connections, in order to support the proposed
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architecture. Ensure that, at a minimum, there are at
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least two diverse network connections coming into each
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rack.</para>
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</listitem>
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</varlistentry>
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</variablelist>
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<para>The selection of form factors or architectures affects the selection
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of server hardware. Ensure that the selected server hardware
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is configured to support enough storage capacity (or storage
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expandability) to match the requirements of selected scale-out
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storage solution. Similarly, the network architecture impacts
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the server hardware selection and vice versa.</para>
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<section xml:id="selecting-storage-hardware">
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<title>Selecting storage hardware</title>
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<para>Determine storage hardware architecture by
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selecting specific storage architecture. Determine the selection of
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storage architecture by evaluating possible solutions against the
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critical factors, the user requirements, technical
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considerations, and operational considerations.
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Incorporate the following facts into your storage architecture:</para>
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<variablelist>
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<varlistentry>
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<term>Cost</term>
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<listitem>
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<para>Storage can be a significant portion of the
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overall system cost. For an organization that is concerned
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with vendor support, a commercial storage solution is
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advisable, although it comes with a higher price
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tag. If initial capital expenditure requires
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minimization, designing a system based on commodity
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hardware would apply. The trade-off is potentially
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higher support costs and a greater risk of
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incompatibility and interoperability issues.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>Scalability</term>
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<listitem>
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<para>Scalability, along with expandability, is a major
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consideration in a general purpose OpenStack cloud. It
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might be difficult to predict the final intended size
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of the implementation as there are no established
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usage patterns for a general purpose cloud. It might
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become necessary to expand the initial deployment in
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order to accommodate growth and user demand.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>Expandability</term>
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<listitem>
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<para>Expandability is a major architecture factor for
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storage solutions with general purpose OpenStack
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cloud. A storage solution that expands
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to 50 PB is considered more expandable than a
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solution that only scales to 10 PB. This meter
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is related to scalability, which is the measure of a
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solution's performance as it expands.</para>
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</listitem>
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</varlistentry>
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</variablelist>
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<para>Using a scale-out storage solution with direct-attached
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storage (DAS) in the servers is well suited for a general
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purpose OpenStack cloud. Cloud services requirements determine
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your choice of scale-out solution. You need to determine if
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a single, highly expandable and highly vertical, scalable,
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centralized storage array is suitable for your design.
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After determining an approach, select the storage hardware
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based on this criteria.</para>
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<para>This list expands upon the potential impacts for including a
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particular storage architecture (and corresponding storage
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hardware) into the design for a general purpose OpenStack
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cloud:</para>
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<variablelist>
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<varlistentry>
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<term>Connectivity</term>
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<listitem>
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<para>Ensure that, if storage protocols
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other than Ethernet are part of the storage solution,
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the appropriate hardware has been selected.
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If a centralized storage array is selected, ensure
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that the hypervisor will be able to connect to that
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storage array for image storage.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>Usage</term>
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<listitem>
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<para>How the particular storage architecture will
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be used is critical for determining the architecture.
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Some of the configurations that will influence the
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architecture include whether it will be used by the
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hypervisors for ephemeral instance storage or if
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OpenStack Object Storage will use it for object storage.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>Instance and image locations</term>
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<listitem>
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<para>
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Where instances and images will be stored will influence
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the architecture.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>Server hardware</term>
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<listitem>
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<para>If the solution is a scale-out
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storage architecture that includes DAS, it
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will affect the server hardware selection. This could
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ripple into the decisions that affect host density,
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instance density, power density, OS-hypervisor,
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management tools and others.</para>
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</listitem>
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</varlistentry>
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</variablelist>
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<para>General purpose OpenStack cloud has multiple options.
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The key factors that will have an influence
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on selection of storage hardware for a general purpose
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OpenStack cloud are as follows:</para>
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<variablelist>
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<varlistentry>
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<term>Capacity</term>
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<listitem>
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<para>Hardware resources selected for the resource nodes
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should be capable of supporting enough storage for the
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cloud services. Defining the initial requirements and
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ensuring the design can support adding capacity is
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important. Hardware nodes selected for object storage
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should be capable of support a large number of inexpensive
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disks with no reliance on RAID controller cards.
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Hardware nodes selected for block storage should be capable
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of supporting high speed storage solutions and RAID controller
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cards to provide performance and redundancy to storage at a
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hardware level.
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Selecting hardware RAID controllers that automatically repair
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damaged arrays will assist with the replacement and repair of
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degraded or destroyed storage devices.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>Performance</term>
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<listitem>
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<para>Disks selected for object storage services do not need
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to be fast performing disks. We recommend that object storage
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nodes take advantage of the best cost per terabyte available
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for storage. Contrastingly, disks chosen for block storage
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services should take advantage of performance boosting
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features that may entail the use of SSDs or flash storage
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to provide high performance block storage pools. Storage
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performance of ephemeral disks used for instances should
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also be taken into consideration.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>Fault tolerance</term>
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<listitem>
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<para>Object storage resource nodes have
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no requirements for hardware fault tolerance or RAID
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controllers. It is not necessary to plan for fault
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tolerance within the object storage hardware because
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the object storage service provides replication
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between zones as a feature of the service. Block
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storage nodes, compute nodes, and cloud controllers
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should all have fault tolerance built in at the
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hardware level by making use of hardware RAID
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controllers and varying levels of RAID configuration.
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The level of RAID chosen should be consistent with the
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performance and availability requirements of the
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cloud.</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</section>
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<section xml:id="selecting-networking-hardware">
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<title>Selecting networking hardware</title>
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<para>Selecting network architecture determines which network
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hardware will be used. Networking software is determined by
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the selected networking hardware.</para>
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<para>There are more subtle design impacts that need to be considered.
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The selection of certain networking hardware (and the networking software)
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affects the management tools that can be used. There are
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exceptions to this; the rise of <emphasis>open</emphasis> networking software
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that supports a range of networking hardware means that there
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are instances where the relationship between networking
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hardware and networking software are not as tightly defined.</para>
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<para>Some of the key considerations that should be included in
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the selection of networking hardware include:</para>
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<variablelist>
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<varlistentry>
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<term>Port count</term>
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<listitem>
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<para>The design will require networking
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hardware that has the requisite port count.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>Port density</term>
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<listitem>
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<para>The network design will be affected by
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the physical space that is required to provide the
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requisite port count. A higher port density is preferred,
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as it leaves more rack space for compute or storage components
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that may be required by the design. This can also lead into
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concerns about fault domains and power density that
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should be considered. Higher density switches are more
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expensive and should also be considered, as it is
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important not to over design the network if it is not
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required.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>Port speed</term>
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<listitem>
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<para>
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The networking hardware must support the proposed
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network speed, for example: 1 GbE, 10 GbE, or
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40 GbE (or even 100 GbE).</para>
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</listitem>
|
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</varlistentry>
|
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<varlistentry>
|
|
<term>Redundancy</term>
|
|
<listitem>
|
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<para>The level of network hardware redundancy
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required is influenced by the user requirements for
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high availability and cost considerations. Network
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redundancy can be achieved by adding redundant power
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supplies or paired switches. If this is a requirement,
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the hardware will need to support this configuration.</para>
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</listitem>
|
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</varlistentry>
|
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<varlistentry>
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<term>Power requirements</term>
|
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<listitem>
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<para>Ensure that the physical data
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center provides the necessary power for the selected
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network hardware.</para>
|
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<note>
|
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<para>
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This may be an issue for spine switches in a leaf and
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spine fabric, or end of row (EoR) switches.</para>
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|
</note>
|
|
</listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
<para>There is no single best practice architecture for the
|
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networking hardware supporting a general purpose OpenStack
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cloud that will apply to all implementations. Some of the key
|
|
factors that will have a strong influence on selection of
|
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networking hardware include:</para>
|
|
<variablelist>
|
|
<varlistentry>
|
|
<term>Connectivity</term>
|
|
<listitem>
|
|
<para>All nodes within an OpenStack cloud
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require network connectivity. In some
|
|
cases, nodes require access to more than one network
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|
segment. The design must encompass sufficient network
|
|
capacity and bandwidth to ensure that all
|
|
communications within the cloud, both north-south and
|
|
east-west traffic have sufficient resources
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available.</para>
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|
</listitem>
|
|
</varlistentry>
|
|
<varlistentry>
|
|
<term>Scalability</term>
|
|
<listitem>
|
|
<para>The network design should
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encompass a physical and logical network design that
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|
can be easily expanded upon. Network hardware should
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|
offer the appropriate types of interfaces and speeds
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|
that are required by the hardware nodes.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
<varlistentry>
|
|
<term>Availability</term>
|
|
<listitem>
|
|
<para>To ensure that access to nodes within
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the cloud is not interrupted, we recommend that
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|
the network architecture identify any single points of
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|
failure and provide some level of redundancy or fault
|
|
tolerance. With regard to the network infrastructure
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|
itself, this often involves use of networking
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protocols such as LACP, VRRP or others to achieve a
|
|
highly available network connection. In addition, it
|
|
is important to consider the networking implications
|
|
on API availability. In order to ensure that the APIs,
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and potentially other services in the cloud are highly
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|
available, we recommend you design a load balancing
|
|
solution within the network architecture to
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accommodate for these requirements.</para>
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|
</listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
</section>
|
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|
|
<section xml:id="software-selection">
|
|
<title>Software selection</title>
|
|
<para>Software selection for a general purpose OpenStack
|
|
architecture design needs to include these three areas:</para>
|
|
<itemizedlist>
|
|
<listitem>
|
|
<para>Operating system (OS) and hypervisor</para>
|
|
</listitem>
|
|
<listitem>
|
|
<para>OpenStack components</para>
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|
</listitem>
|
|
<listitem>
|
|
<para>Supplemental software</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
</section>
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<section xml:id="os-and-hypervisor">
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<title>Operating system and hypervisor</title>
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<para>The operating system (OS) and hypervisor have a
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|
significant impact on the overall design. Selecting a particular
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|
operating system and hypervisor can directly affect server
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|
hardware selection. Make sure the storage
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|
hardware and topology support the selected operating
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|
system and hypervisor combination. Also ensure the networking
|
|
hardware selection and topology will work with the chosen operating
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|
system and hypervisor combination.</para>
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<para>Some areas that could be impacted by the selection of OS and
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|
hypervisor include:</para>
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<variablelist>
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|
<varlistentry>
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|
<term>Cost</term>
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<listitem>
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|
<para>Selecting a commercially supported hypervisor,
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|
such as Microsoft Hyper-V, will result in a different
|
|
cost model rather than community-supported open source
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|
hypervisors including <glossterm
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baseform="kernel-based VM (KVM)">KVM</glossterm>,
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|
Kinstance or <glossterm>Xen</glossterm>. When
|
|
comparing open source OS solutions, choosing Ubuntu
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|
over Red Hat (or vice versa) will have an impact on
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|
cost due to support contracts.</para>
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|
</listitem>
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|
</varlistentry>
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|
<varlistentry>
|
|
<term>Supportability</term>
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|
<listitem>
|
|
<para>Depending on the selected
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|
hypervisor, staff should have the appropriate
|
|
training and knowledge to support the selected OS and
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|
hypervisor combination. If they do not, training will
|
|
need to be provided which could have a cost impact on
|
|
the design.</para>
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|
</listitem>
|
|
</varlistentry>
|
|
<varlistentry>
|
|
<term>Management tools</term>
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|
<listitem>
|
|
<para>The management tools used for
|
|
Ubuntu and Kinstance differ from the management tools
|
|
for VMware vSphere. Although both OS and hypervisor
|
|
combinations are supported by OpenStack, there will be
|
|
very different impacts to the rest of the design as a
|
|
result of the selection of one combination versus the
|
|
other.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
<varlistentry>
|
|
<term>Scale and performance</term>
|
|
<listitem>
|
|
<para>Ensure that selected OS and
|
|
hypervisor combinations meet the appropriate scale and
|
|
performance requirements. The chosen architecture will
|
|
need to meet the targeted instance-host ratios with
|
|
the selected OS-hypervisor combinations.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
<varlistentry>
|
|
<term>Security</term>
|
|
<listitem>
|
|
<para>Ensure that the design can accommodate
|
|
regular periodic installations of application security
|
|
patches while maintaining required workloads. The
|
|
frequency of security patches for the proposed
|
|
OS-hypervisor combination will have an impact on
|
|
performance and the patch installation process could
|
|
affect maintenance windows.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
<varlistentry>
|
|
<term>Supported features</term>
|
|
<listitem>
|
|
<para>Determine which features of OpenStack are required.
|
|
This will often determine the selection of the OS-hypervisor combination.
|
|
Some features are only available with specific operating systems or
|
|
hypervisors.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
<varlistentry>
|
|
<term>Interoperability</term>
|
|
<listitem>
|
|
<para>You will need to consider how the OS and hypervisor combination
|
|
interactions with other operating systems and hypervisors, including
|
|
other software solutions.
|
|
Operational troubleshooting tools for one OS-hypervisor
|
|
combination may differ from the tools used for another OS-hypervisor
|
|
combination and, as a result, the design will need to
|
|
address if the two sets of tools need to interoperate.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
</section>
|
|
|
|
<section xml:id="openstack-components">
|
|
<title>OpenStack components</title>
|
|
<para>Selecting which OpenStack components are included in the overall
|
|
design is important. Some OpenStack components, like
|
|
compute and Image service, are required in every architecture. Other
|
|
components, like Orchestration, are not always required.</para>
|
|
<para>Excluding certain OpenStack components can limit or constrain
|
|
the functionality of other components. For example, if the architecture includes
|
|
Orchestration but excludes Telemetry, then the design will not be able
|
|
to take advantage of Orchestrations' auto scaling functionality.
|
|
It is important to research the component interdependencies
|
|
in conjunction with the technical requirements before deciding
|
|
on the final architecture.</para>
|
|
|
|
<section xml:id="networking-software">
|
|
<title>Networking software</title>
|
|
<para>OpenStack Networking (neutron) provides a wide variety of networking
|
|
services for instances. There are many additional networking
|
|
software packages that can be useful when managing OpenStack
|
|
components. Some examples include:</para>
|
|
<itemizedlist>
|
|
<listitem>
|
|
<para>
|
|
Software to provide load balancing
|
|
</para>
|
|
</listitem>
|
|
<listitem>
|
|
<para>
|
|
Network redundancy protocols
|
|
</para>
|
|
</listitem>
|
|
<listitem>
|
|
<para>
|
|
Routing daemons
|
|
</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
<para>Some of these software packages are described
|
|
in more detail in the <citetitle>OpenStack High Availability
|
|
Guide</citetitle> (refer to the <link
|
|
xlink:href="http://docs.openstack.org/ha-guide/networking-ha.html">Network
|
|
controller cluster stack chapter</link> of the OpenStack High
|
|
Availability Guide).</para>
|
|
<para>For a general purpose OpenStack cloud, the OpenStack
|
|
infrastructure components need to be highly available. If
|
|
the design does not include hardware load balancing,
|
|
networking software packages like HAProxy will need to be
|
|
included.</para>
|
|
</section>
|
|
|
|
<section xml:id="management-software">
|
|
<title>Management software</title>
|
|
<para>Selected supplemental software solution impacts and
|
|
affects the overall OpenStack cloud design. This includes
|
|
software for providing clustering, logging, monitoring and
|
|
alerting.</para>
|
|
<para>Inclusion of clustering software, such as Corosync or
|
|
Pacemaker, is determined primarily by the availability
|
|
requirements. The impact of including (or not
|
|
including) these software packages is primarily determined by
|
|
the availability of the cloud infrastructure and the
|
|
complexity of supporting the configuration after it is
|
|
deployed. The <link xlink:href="http://docs.openstack.org/high-availability-guide/"><citetitle>OpenStack High Availability Guide</citetitle></link>
|
|
provides more
|
|
details on the installation and configuration of Corosync and
|
|
Pacemaker, should these packages need to be included in the
|
|
design.</para>
|
|
<para>Requirements for logging, monitoring, and alerting are
|
|
determined by operational considerations. Each of these
|
|
sub-categories includes a number of various options.</para>
|
|
<para>If these software packages are required, the
|
|
design must account for the additional resource consumption
|
|
(CPU, RAM, storage, and network bandwidth). Some other potential
|
|
design impacts include:</para>
|
|
<itemizedlist>
|
|
<listitem>
|
|
<para>OS-hypervisor combination: Ensure that the
|
|
selected logging, monitoring, or alerting tools
|
|
support the proposed OS-hypervisor combination.</para>
|
|
</listitem>
|
|
<listitem>
|
|
<para>Network hardware: The network hardware selection
|
|
needs to be supported by the logging, monitoring, and
|
|
alerting software.</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
</section>
|
|
|
|
<section xml:id="database-software">
|
|
<title>Database software</title>
|
|
<para>OpenStack components often require access
|
|
to back-end database services to store state and configuration
|
|
information. Selecting an appropriate back-end database
|
|
that satisfies the availability and fault tolerance
|
|
requirements of the OpenStack services is required. OpenStack
|
|
services supports connecting to a database that is supported
|
|
by the SQLAlchemy python drivers, however, most common
|
|
database deployments make use of MySQL or variations of it. We
|
|
recommend that the database, which provides back-end
|
|
service within a general purpose cloud, be made highly
|
|
available when using an available technology which can
|
|
accomplish that goal.</para>
|
|
</section>
|
|
</section>
|
|
</section>
|